Bacteria from the genera Bacillus and Clostridium produce unusually durable endospores that are the infectious agent of Anthrax and Botulism. The phagocytosis-like process of engulfment is the hallmark of endospore formation, as it creates the unique cell within a cell structure that allows spore assembly to occur within the cytoplasm. However, it has remained unclear how bacterial cells evolved the ability to perform engulfment given the simplicity of their cellular machinery and the seemingly insurmountable barrier presented by the cell wall that surrounds bacterial cells. Our studies suggest that membrane migration during engulfment is mediated by one essential protein machinery, the SpoIID/SpoIIM/SpoIIP complex that degrades the bacterial cell wall, plus two partially redundant machineries, the SpoIIQ-SpoIIIAH complex that provides a zipper-like adhesion between the developing cells and peptidoglycan biosynthesis which is essential for membrane migration when SpoIIQ is absent. The final step of engulfment, membrane fission, requires both ongoing peptidoglycan biogenesis and SpoIIIE, which is also required for the final stages of chromosome segregation and septal membrane fission during the asymmetrically positioned cell division event of sporulation. We will take a combined cell biological, genetic and biochemical approach to study the spatial regulation of peptidoglycan degradation and synthesis, the protein-protein interactions that mediate engulfment, and to understand the mechanisms by which bacterial cells catalyze membrane fission and are dynamically organized. Engulfment provides a dispensable system to study cell biological events that are essential for all bacteria, such as protein localization and membrane fusion.